Electrical telemetry



March 16, 1937. v w R SCHQFIELD. JR 2,073,948

ELECTRICAL TELEMETRY Filed June 14, 1933 7 Sheets-Sheet 1 INVENTOR. Y )YMQMM, M 3.61.26;

f4 ATTORNEY.

16, 1937. w. R SCHQFIELD. JR 2,073,948

ELECTRICAL TELEMETRY Filed June 14, 1933 Sheets- -Sheet 2 INVENTOR. BY we? QLW MRLEBM 26,1 ATTORNEY.

March 16, 1937.

Filed June 14, 1933 7 Sheets-Sheet 3 2 6 s Ej;[f L g1 F 4 WNW M v w FY T I'J 21 31a 24 e l 38 24 37 INVENTOR. 2 $1 M 1 ATTORNEY.

March 16, 1937. w. R. SCHOFIELD,.JR 2,073,943

ELECTRICAL TELEMETRY Filed June 14, 1955 -7'Sh eets-S h:eet 4 INVENTOR. v )AZLW L 1/ M A TTORNEY.

March 16, 193% w, R, SCHOFIELD, JR" 2,073,948

ELECTRICAL TELEMETRY Filed June 14, 1933 7 Sheets-Sheet 5 F INVENTOR. PAQ QM i MW f BY March 16, 1937. w. R SCHOFIELD. JR 9 9 ELECTRICAL TELEMETRY Filed June 14, 1933 7 Sheets-Sheet 6 15 ATTORNEY.

March 16, 1937; w, R H FIELD, JR 2,073,948

ELECTRICAL TELEMETRY Filed June 14, 1933 7 Sheets-Sheet 7 I u i I H k v i My INVENTOR.

U1 W1 BY 2 ATTORNEY.

Patented Mar. 16, 1 937 PATENT OFFICE ELECTRICAL TELEMETRY William R. Schofield, J12, Philadelphia, Pa., assignor to Leeds & Northrup Company, Philadelphia, Pa., a corporation of Pennsylvania Application June 14, 1933, Serial No. 675,705

18 Claims.

My invention relates to electricalsystems for determining or recordingat a receiving station, the magnitude or changes of a condition at a more or less remote transmitting station.

In systems of this character, it has not heretofore been possible to ascertain all positions of the transmitting element when that element was capable of at least 360 of movement, or more specifically, of making unlimited number of revom lutions in one or both directions.

In accordance with my invention, the trans: mitting slide-wire is greater than 360 in extent, and preferably is comprised of sections less than 360 in extent with their ends staggered or over- Is lapping, and the cooperating contact structure is .divided into elements selectively connected to the transmission line between stations by switching mechanism which is preferably controlled by the transmitting element.

My invention also resides in the features of construction, combination and arrangement hereinafter described and claimed.

For an understanding of my'invention and for illustration of various modifications thereof, ref erence is to be had to the accompanying drawings in which:

Fig. 1 illustrates diagrammatically an electrical measuring system.

Fig. 2, in perspective, illustrates apparatus adapted to be included in the system of Fig. 1

Fig. 3 diagrammatically illustrates a Wheatstone bridge system utilizing the invention.

Fig. 4, partly in perspective, illustrates indieating and recording mechanism. 7

Fig. 5 diagrammatically illustrates another type of indicator.

Fig. 6 diagrammatically illustrates apparatus for transmitting indication of a liquid level.

Fig. 6a illustrates a modification affording tem- 4 perature compensation.

Fig. '7 illustrates a system utilizing the invention for determination of integrated and frac tional revolutions. 1

Fig. 8 illustrates another modification for re- 45 cording integrated and fractional revolutions and Referring to Fig. 1 the transmitting slide wire S comprises two sections SI, $2, each less than 360 in extent, butstaggered so that each section bridges or overlaps the discontinuity or gap of the other. By way of example, the slide wire sections may each enclose 90% of a circle and may be displaced 30%, as shown by Fig. 1. The cooperating contact structure C consists of the contact elements Cl and C2 which engage the slide wires SI, S2 respectively. The resistance R connected between the low potential end of the section S2 and the point N of the network, and the resistance RI connected between the high potential end of the slide-wire section SI and the point P of the network are of such value that from 30 to 90, the contact elements Cl, C2, are simultaneously at the same potential.

The change of magnitude of the condition to be measured, for example temperature, wind direction, pressure, etc., effects in any known manner relative movement between the slide wife and its contact structure, i. e., the slide wire may move with respect to the contact structure Cl, C2 or vice versa. In either case, the range of relative rotation may be more than one revolution, or in fact an unlimited number of revolutions in someinstances. Assuming for. purposes of explanation that the contacts are movable with respect to the slide wire, the two contact elements Cl, C2 are movable as a unit about the axis A, the contacts remaining in fixed position relative to each other.

Between the points P and N are connected a suitable source of current B and a resistance R2 adjustable to regulate the current flowing through the slide wire as indicated by meter M so that it corresponds to the value for which the slide wire is calibrated. The receiving station may comprise a receiving slidewire S3 connected across a suitable source of current Bl, in series with a resistance R3 for adjusting the slide wire current as indicated by the meter Ml to the value for which the slide wire scale I is callbrated.

The operation of the system is as follows:

Assume that the magnitude of temperature, pressure or other condition under measurement is such that the contact CI engages slide-wire section SI at zero, and is connected by contact 2 of the double throw switch 3 tov conductor 4 of the transmission line 4, 4' which extends between the transmitting and receiving stations. For this position of the contact structure of the transmitting slide wire, the galvanometer G gives zero deflection indicating balance of the the new magnitude of the measured condition.

It is apparent that if the contact 2 of the switch 3 remains in the position indicated in Fig. 1, that when contact CI is moved beyond point 90 of slide wire SI any position of contact C3 of the receiving slide wire would indicate a false balance due to an opening in the galvanom-' eter circuit G. Therefore, suitably before the contact CI reaches this point, say, for example, at about 85% of a revolution from the zero point,

switch 3 is operated, manually at the receivingstation, or preferably automatically at the transmitting station as hereinafter described, to disconnect the conductor 4 from contact CI and to connect it to the contact C2. As the two contacts CI and C2 at this time are at points of the same potential on the different slide wires SI and S2, the transition from one to the other effected by operation of switch 3 does not require change in position of the contact C3 for balance, or if an automatic recorder is used, the transition causes no disturbance of the record.

Assuming that the contact structure continues to rotate in counter-clockwise direction, the slide wire S2 continues in circuit until switch 3 is again operated to connect conductor 4 to contact CI which is eflected suitably before the contact structure reaches point I20 of slide wire S2,-for

example at about H5. This transition requires a change in position of contact C3, 1, e., for the specific example given, the contact would need to be moved down 100 units on scale I. Further rotation in the same direction repeats this cycle; rotation in reverse direction, simply reverses the order of the transitions. 45 Therefore the position of the contact structure C, which corresponds to the position of an element following or responsive to the changes of a condition, can be determined throughout its full 360 degrees of movement for either direction of movement, and for unlimited angular movement in either direction. For each position of contacts CI and C2 within thesector of overlap of the high potential and low potential ends of the transmitting slide-wire, there are two possible positions of balance of contact C3 of the receiving slide-wire depending upon which of contacts CI, C2 is connected to the link circuit. Fig. 2 illustrates an arrangement in which the contact structure is moved bya weather .vane 5, which is illustrative of an instrument in which the primary transmitting element may rotate in either direction for an unlimited number of revolutions. An anti-aircraft gun turret is another example of such an element. The arm 6 which 65 carries the contact structure of the transmitting slide wire rotates with the shaft I of the vane. The disk 8 carries contact rings, as shown, engaged by the contacts CI, C2 for connecting them to the stationary contacts of switch 3. .As an alternative the contact structure may be fixed to y a suitable stationary support, and the slide wire disk 8 secured to shaft I. The movable contact 2 of the switch 3 is adapted to be operated from the shaft I, automatically to effect the transi- 75 tion from one slide wire section to the other to ensure continuity of the circuit between the transmitting and receiving slide-wires, and preferably there is interposed a lost motion device so that if the switch is operated for movement of .the shaft I in onedirection, it will not be operated at the same position of the shaft for movement of the shaft in a reverse direction, thus avoiding unnecessary operation of switch 3. Furthermore, the provision of thislost motion has the advantage that when the slide contact structure C is swinging within the range of about 100 to 120 the contact C3 of the receiving slide wire need not so often be shifted from one end to the other of the slide wire, or in the case of an automatic recorder, unnecessary oscillations of the recorder needle and the automatic rebaiancing direction as viewed in Fig. 2, the pin I6 engages one of the projections of the star wheel l5 and tensions the spring I3. when the torque of spring I3 is increased by movement of shaft I sufficiently to,overcome the spring I2, pawl II is forced from the notch and allows contact 2 quickly to move through a quarter revolution,

whereupon the pawl II drops into the next notch to arrest further movement. The actuation of the movable contacteifects disconnection of contact C2 from conductor 4 and effects connec ion of contact Cl. Assuming that the shaft I ontinues movement in clockwise direction, the econd pin I'I engages projection of the star wheel I5 and efiects another operation of switch 2. The spacing between the pins I6 and I1 is so related to the extent of displacement or staggering of the slide wire section, that the switch 2 is operated to ensure continuity of the circuit between galvanometer G and the slide wire, i. e., as the contact in 'circuit approaches the discontinuity of its slide wire, the switch is operated to connect the other slide wire in circuit as previously described. v

It is therefore possible at all times accurately to determine the wind direction at the receiving station.

Since thestarwheel I5 in the construction illustrated must be rotated through a considerable angle before effecting operation of switch 2, the switch 2 will not repeatedly operate if the shaft I oscillates back and forth within a narrow range, i. e., the mechanism described shifts the points at which the switch 2 is operated for opposite directions of rotation of shaft I; for example, the switch may operate at 85% and 115%" of a revolution for clockwise movement of the shaft I, whereas for counter-clockwise movement the switch will operate at, for example, 75% and 105%; that is to say, the transfer point from slide wire SI to slide wire S2below 100% when rotating in one direction may be 10% higher than the transfer point of slide wire S2 to slide wire SI in the decreasing direction; similarly, the transfer point from S2 to SI in the increasing direction may be 10% higher above-100% of a revolution, than the return transfer from Si to S2, when decreasing.

scale may be calibrated with north, for example,

' at the low end of the scale, followed by east, south,

Y west, north, and ending with east, or south, de-

pending upon the extent sections SI, S2.

Referring to Fig. 3.there is illustrated a modification using the device of Fig. 2 in a Wheatstone bridge type of balanced network. The selected slide-wire section Sl-S2 is included in two arms of overlap of slide wire of the bridge, the position of the slide wire contact c determining the proportion included in each arm. A second slide wire S3 is included in the other two arms of the bridge, adjustment of its contact C3 permitting balance of the galvanometer G. In order that the measurements shall be substantially independent of the resistance of the leads, the bridge is preferably of the type shown in Leeds Patent 1,097,651, and accordingly there is provided the resistance 54 whose contact C4 is adjustable in unison with the contact C3 of the slide wire S3. The network may be energized by current from battery Bl, or other direct current source, or by alternating current. In the latter case, galvanometer G is an alternating current instrument and its field is excited by current from the same source.

The two slide wire sections SI, S2 are in parallel between the conjugate points N, P'of the slide wire is the same as in Fig. 1, i. e., as the con- 4 tact in CI or C2 circuit approaches the discon tinuity of the slide wire section with which it is in engagement, the switch 3 is operated to change over to the other contact whose associated slide wire bridges the discontinuity or gap.

Fig. 4 illustrates a known type of self-balancing mechanism suitable for use at the receiving station; specifically it is of the type described in Leeds Patent 1,125,699.

Briefly, upon the controlled shaft l9 there is mounted the slide wire S3, of Fig.1, or the slide wires S3 and S4 of Fig. 3. The needle 20 of the galvanometer G in response to unbalance of the network, including the transmitting and receiving slide wires and the link or transmission circuit between them, deflects in one direction or the other to effect corresponding displacement of the driving clutch member 2| while free of the driven clutch member 22 secured to shaft l9. Thereafter, in the cycle of operation, the driving clutch member 2| while in engagement with the driven clutch member 22 is returned by one or the other of the cams 23 secured to shaft 24 driven by motor 25, to its horizontal or neutral position eflecting movement of the slide wirerelative to its contact to rebalance the network.

The marker or recorder pen 26 is driven from the controlled shaft l9 through the pulley 21 and cord 28 to trace upon the record sheet la, the variations or changes in magnitude of the condition determining or controlling the position of the contact structure C of the transmitting slide wire.

For many uses, it is desirable to integrate the number of revolutions of shaft 1 of the transmitting slide wire; for example, referring to" Fig. 6, the shaft 1 may be driven through suitable mechanism diagrammatically illustrated by the float 30 for measuring the level of liquid in j the tank 3| which generically represents a tank, well, stream, or the like. In moving from its maximum to minimum po ition, the float 30 may effect several revolutions of the shaft 1. To assume a specific instance for purposes of explanation, the float 30 may move through a distance of feet, and the connections to shaft 1 may be such that the shaft 1 is rotated through ten revolutions. With the apparatus of Fig. 4, as thus far described, used with the transmitting system of Fig. 1, or of Fig. 2, the pen 26 will indicate the position of shaft 1 but'will not distinguish between the revolutions, i. e., it will give the indication 6, for example, for 6 feet, lfi'feet, 26 feet, etc. Accordingly it is desirable to add an' attachment which will distinguish between such with a contact 3la which when the pen-reaches a position corresponding to one transition pointof the transmitting slide wire, say revolu-- tion, closes the circuit of a solenoid 32, or equiva lent, to effect movement of armature 33 to advance the star wheel 34, or equivalent, one tooth, to shift the indicating or printing wheel 35 to the next highest number. Accordingly, as the float rises, each time the pen contact 3la bridges the contacts 36,31, the wheel 35 is stepped to the next higher number, 10, 20, 30, etc. Similarly when the pen, in following the balancing of the network, reaches a position at which the other transition of the transmitting slide wire is effected, for example 5% revolution, the contact 3Ia of the pen engages the contacts 38, 39 to en-- ergize the solenoid 40 which attracts armature 4| to effect reverse movement of the indicating wheel 35, by one step, for falling movement of the float. Accordingly, the step by step mechanism integrates the number of complete revolutions of shaft 1, and pen 26 accurately indicates the position of shaft 1 for indication of fractional parts of a complete revolution.

The same end may be accomplished, by using instead of the step by step mechanism described, a second transmitting slide wire S5 suitably driven from shaft! so that its contact C1 moves from one end of the slide wire S5 to the other for the total range of movement of float 30; and this slide wire may be connected to a separate recorder of the type shown in'Fig. 4. The pen of such recorder would travel across'the scale only once for movement of the float 30 from maximum to minimum position, and the recorder connected to the slide wire S would serve as a vernier.

Another integrating arrangement is shown in Fig. 5. The step by step mechanism in this instance is actuated by movement of the contact of the transmitting slide wire, rather than by response of the receiving slide-wire apparatus. The recorder of Fig. 4, or equivalent, may be used for determining the position of the shaft 1 within the limits of a revolution, and the mechanism .now described is for indicating the number of revolutions, adding for movement of shaft 1 in one direction, and subtracting for movement of shaft 1 in reverse direction.

. The shaft 43 is connected to a suitable revolution counter 44, the hand 45 making for example one revolution for each tenrevolutions of shaft 43 in one direction, and the hand 46 moving for example, one graduation for each complete revolution of hand 45. This relation can be efiected in any known manner common to counting trains, for example, by use of Geneva wheels, or gearing of suitable ratio.

The polarized relays 41, 48 are connected to th conductors 49, flow of current in 'one direction eifecting movement of the armature 56 of relay 48 to advance the star wheel one step, and flow of current in reverse direction effecting movement of armature 52 of relay 41 to move the star wheel 53 one step in the reverse direction.

The relays are controlled by a current reversing switch 54 consisting of the contacts 55, 56

having extensions projecting in the path of movement of the pin l1, and contacts 58, 59 having extensions disposed in the path of movement of the pin 60. The pins l1 and 69 are carried by the contact arm l8, and therefore the positions of these pins in space are definitely related to the position of the contact structure of the transmitting slide wire. All of the contacts 55, 56, 58, 59 are normally open. Each time the shaft 1 completes a revolution in a clockwise dishaft 1 in counter-clockwise direction, the pin 60 effects momentary closure of the switches 58, 59 which effects flow of current from battery B2 :through conductors 49 in reverse direction to effect energization of the relay 41 which notches the shaft 43 one step in reverse or negative direction. The contacts are so located that 55,

56 are closed by pin l1 as pen 26 or equivalent reaches for example, point "ll of the recorder scale, and contacts 58, 59 are closed by pin 66 as the pen in reverse direction fpames point 99 of the scale.

The combination of the recorder of Fig. 4 and an indicating device such as shown in Fig. 5,

- permits the position of the float to be determined with great nicety throughout very large range of total float movement; for example, the position of the float may be accurately determined to within a. small fraction of an inch throughout .a range of movement of many feet. Accuracy of high order is of prime importance when, for example, the tank 3| is a storage tank for'large bodies of gasoline or other valuable liquid, as it -is necessary that the metering of addition or removal of fluid be very precise.

', cause of variation in length of the cable with change, of temperature; i. e., increase in length of the cable due to increase of temperature has the same effect upon the position of shaft 1 as an increase inheight ofthe liquid level and vice versa. This error may be compensated by the Y arrangement shown in Fig. 6a so that the accuracy The Wheatstone bridge W includes in one arm 1 thereof the resistance R6 of material having a suitably high temperature coeflicient, for example,

copper or nickel, and the other resistances R1-R9, of maganin or other metal of negligible temperature coeflicient, are preferably so proporthrough the resistance RIO which is in one con-- one end of the resistance to the other for movement of the float from one extreme of its range to the other. Therefore the position ofthe contact from the point N is proportionalto the active length of cable between the float and the pulley 62, and the drop of potential between the point N and contact Clo is proportional to the unbalance of the bridge, or temperature. The conductor 4' of the link circuit, instead of being connected directly to the point N as in Fig. 1, is connected to the contact CH) of resistance RIB so that the potential difi'erence between the conductors 4 and 4', which is impressed upon the receiving slide wire, is the algebraic sum of the voltages between the point N and contact CH), and between point N and contact Cl or C2 depending upon which of the latter two is in circuit; i. e., the total voltage impressed on the transmitting end of the link circuit includes as a component a voltage proportional to temperature and the active length of cable.

Referring to Fig. 7, which illustrates another system utilizing the invention, when the contacts 63, 64 are in the position indicated, in engagement with contacts 65, 65, the circuit is substantially the same as in Fig. 3 and the same reference characters are used to identify like elements of the system: when contacts 63, 64 are in their upper position in engagement with contacts 61,68, the slide wire S5 is substituted for the slide wire S, i. e., the two arms of the bridge at the transmitting end are then comprised of This system is adapted for use withthearrangement shown in Fig. 6 in which slide wire S5 makes one revolution for the total travel of float 39 and shaft 1 of slide wire S makes several revolutions. With contacts 63, 64 in their upper position the bridge is balanced roughly to determine the position of float 30; i. e., to ascertain whether it is between say the limits 30 and 40 feet or between 10 and 20 feet; and with the contacts 63, 64 in the lower position, the location of the float within those limits is precisely determinable.

Preferably, to minimize the number of wires between the transmitting and receiving stations, contacts 63, 64 are located at the transmitting station and their change over is eflected from or at the receiving station by utilizing the link circuit conductors. Specifically, the polarized relay 69 included in the conjugate lead 4', and its armature 10 is suitably mechanically connected to contacts 63, 64 to move them into engagement with contacts 65, 66 when energized by current of one polarity and to return to engagement with contacts 61, 68 when energized by current of opposite polarity.

' The arrangement at the receiving station for effecting operation of the relay may be similar to that described and claimed in Wunsch applicatidn Serial No. 560,152. Specifically, when the reversing switch 1| operable by handle H is in the position shown with its contact 12 bridging the contacts 13, 14 and its contact 12'bridging the handle is operated so that the contact 13 connected to contact 16 and contact 14 to the portions of S5, on either side of contact C1.

contact 11, current flows from battery B3 through the relay in opposite direction. Therefore by manipulation of. handle 'II' at the receiving 7 station, either slide wire S5, or slide wire S may 5 .be included .in circuit at will; a suitable legend 20 be effected intermittently by cams, or other suit,-

When contacts 12, 12' are in their neutral or' non-bridging positions, the galvanometer is in circuit for determination of the position of contact 0110: of the contact structure of slide wire S. a v

With an automatic recorder, such as shown in Fig. ithe operation of switches II and 15 may able structurey-driven from the shaft 24.. For this type of system, the recorder may be or the two point type, such asdisclosed in "the aforesaid Leeds patent, to distinguish the readings 25 due to slide wire S5 from those of slide wire S.

tem in whichthe transmitting slide wire is of extent greater than 360 to measure with precision fractions of a revolution of a member capable of more than 360 of movement, such as shaft 1 of Fig. 6. When the contacts 18, 19 are 40 in engagement with contacts 82, 83 the slide wire S8 is connected with the link circuit 4, 4', for determination of the integrated revolutions of shaft 1.

The movement of contacts 18, 19 may be effected by their mechanical connection to the star wheel 84 or equivalent, of the electromagnetic step-by-step device 85 having coil 88 and armature 81. The coil 85 as indicated isincluded in one of the conductors of the link circuit 4, 4' but-the feeble unbalance current of the network is insumcient to effect movement of the armature 81. 4

For measuring, the contact 88 is-in engagement with contact 89; to effect actuation of the step-by-step device 85 to shift from slide'wire S5 for measurement of integrated revolutions to slide wire 8 for measurement of the fractional revolution, or vice versa, contact 88 is momentarily moved into engagement with contact 0 88 to connect battery B3 in circuit. Preferably contact 88 is mechanically connected to contact 8| for closing a shunt circuit around galvanometer G to protect it from the relatively heavy current from battery B3. In an automatic re- 5 corder, such as shown in Fig. 4 for example, contact 88 may be actuated periodically as by a cam 92 driven from the shaft 24. 3

For measuring either the position of contact C1, or Cl, C2, the contact C3 of the receiving slide 0 wire isconnected to the link circuit through the movable contact 93 and contact sector 94 of a step-by-step device 85 whose coil 88 effects movement of armature 91 when contact 88 is actuated to include battery B3 in circuit.

75 The step-by-step devices 85 and 95 are synchronlzed so that when contact 93 has moved into engagement with sector 98,'the contacts '18 and 19 are in engagement with contacts 99, I80 whichare connected across the terminals of the transmitting slide wiresS and S5. Therefore, the galvanometer G deflects if there is unbalance between the total available voltages across the receiving and transmitting slide wires. Resistance R3 is adjusted, preferably automatically by mechanism similar to that described in the aforesaid Leeds Patent 1,125,699, until balance is obtained. The receiving slide-wire is in effect recalibrated and there is no need of an v operator or service man travelling to the transmitting station for readjustment of resistance R2 to recalibrate because of variationin voltage of battery B due to aging, etc..

-It is not necessary that the transmitting slide wire S be divided into two sections in order to obtain measurements throughout a complete revolution or more. Referring to Figs. 9 and 10,

the slide wire S is comprised of a single continuous section, suitably greater than 360 with its overlapping ends Se and SE suitably spaced. The contact structure therefor is divided into contact elements CI and C2. Within the angle or sector of overlap, the upper contact Ci, Fig. 10, engages only the end portion SE and the lower contact C2 engages only the lower end portion Se and preferably for substantially the remaining angle, both of the contacts engage the wire which preferably, as shown, is helically wound on disk 8.

The switch 3, not shown in Fig. 10. for clarity, but constructed and operated as above described in connection with Fig. 2, transfers the connection to the link circuit from Cl to C2 before contact CI passes beyond the end of overlapping section SE for counter-clockwise movement of arm l8, and transfers from C2 to Cl before C2 passes beyond overlapping section Se for clockwise movement of the arm,

Operation of this modification can best be understood by consideration of the diagram of .Iig. 9. It is first assumed that the contacts Cl,

C2 are in the dotted line position, both in contact with the slide wire. The resistor RH in series with the slide wire is equal in magnitude to the resistance of the slide wire between contacts Cl, 02 so that the voltage drop between the point X and contact CI is equal to the voltage drop between point Y and contact C2. (The conductor between Y and the end Se of the slide wire is of negligible resistance).

Therefore within the region for which both contacts Cl and C2 are in engagement with the slide wire, the voltage impressed on the link circuit is the same regardless of which of the contacts is connected by switch 3, since the transition from one to the other is accompanied by concurrent shift from point X to point Y; i. e., when contact 2 of switch 3 is in upper position to connect slide wire contact CI to conductor 4, contact 2A of the switch is in position to connect conductor 4' to point X to include the voltage drop across resistor RI I and when contact 2 of switch 3 is in its lower position to connect slide wire contact C2'to conductor 4, contact 2A of switch 3 is in position to connect conductor 4 to the point'Y to exclude the voltage drop across resistor RI I.

There is no position of arm l8 which cannot be determined at the receiving station, regardless of the number of revolutions of shaft 1 in either direction. The slide wire construction ofFig. 10 can be substituted for the two section slide wire of any of the preceding modifications. It is of course immaterial whether the contact structure Cl, C2 is rotatable and the slide wire disc 8 stationary or vice versa.

In all modifications, the transmitting slide wire is more than 360 in angular extent; the receiving slide wire if arcuate may be more or less than 360, or it may be a straight wire or on a straight form; for automatic recording, the receiving slide wire as indicated is usually circular and less than 360.

For simplicity of explanation, batteries have been shown in Figs. 1, 3, 6a, 7, 8, and 9 as sources of current for the measuring network. It is to be understood however, that other sources of current, direct or alternating, may be used. In the modifications using polarized relays batteries B2, (Fig. 5) B3 (Fig. '7) are generically illustrative of any direct current source.

In the potentiometer system shown in Fig. 11, the two overlapping sections Si, S2 of slide wire S are connected in series, as by conductor Cs of negligible resistance, instead of in shunt to each other, as in Figs. 1 and 2 for example. The resistance Rl3 is included and excluded from circuit insofar as impression of its voltage drop upon the link circuit is concerned concurrently with changeover from contact C2 to Cl and vice versa. The resistances Rl3 and RH are of such magnitude that the drop of potential across each of them is equal to diflzerence in potential between points 30 and of either slide wire section. The changeover from contact CI to C2 or vice versa within the range 30-90 does not therefore require or eifect movement of contact C3 since the concurrent inclusion or exclusion of resistance Ri3 by contact In of switch 3 produces a voltage change equal and opposite to that produced by the changeover. In general, the resistance Rl3 has the same purpose as resistance RI I of Fig. 9.

The movement of contact structure C relative to slide wire S is efiected by changes in the condition under measurement, and as in all other modifications, there is no position of the contact structure which does not permit balance of the network regardless of the direction or number of revolutions.

The modifications shown in Fig. 12 is for use with alternating current. The slide wire SS or voltage-dividing impedance is comprised of two coils SSI and SS2, shown for simplicity as wound on separate cores of magnetic material, which coils are the equivalent of the slide wire sections SI, S2 of Fig. l and other modifications. The discontinuities between the terminals of the coils are staggered so that at least one or the other of the contacts Cl, C2 of the movable contact struc-.

ture is at all times in engagement with the slide As in the other modifications switch 3 is operated to ensure connection to the receiving slidewire S3 for all settings of the transmitting wire.

The energizing current for the receiving slidewire is supplied-by transformer BBI for example. Current for the transmitting slidewire is supplied by transformer BB. The proper potentials for the terminal 90 of coil SS! and terminal 30 of coil SS2 may be obtained from the taps 1!, ti of the secondary of transformer BB.

Although the coils are shown in parallel, they may be connected in series as in Fig. 10. The 1 inductive type of slide-wire may also be used in the Wheatstone bridge circuit of Fig. 2.

The mode of operation for any of these arrangements will be understood from the detailed description of the operation of the preceding arrangements.

While I have disclosed specific modifications of my device and illustrated and described certain uses thereof, it is to be understood that my invention is not limited thereto but is co-extensive in scope with the appended claims.

For brevity, the term slide-wire as used in the claims is generic to a voltage-dividing impedance consisting substantially entirely of resistance or of reactance, or having any desired ratio of reactance to resistance.

What I claim is:

1. An electrical measuring system comprising a transmitting station, a receiving station, a link circuit between said stations, a slide wire at said transmitting station extending more than 360 and having a low potential portion overlapping a higher potential portion, contact structure having contact elements for engaging said slide wire, one of said elements engaging said low potential tial portion, structure responsive to changes of a condition for effecting relative rotation of said slide wire and contact structure of more than 360, and switching means for selectively connecting one or the other of said contact elements to said link circuit.

portion while the other engages said high potening contact elements for engaging said slide wire,

one of said elements engaging said low potential portion while the other engages said high potential portion, structure responsive to changes of a condition for effecting relative rotation of said slide wire and contact structure of more than 360, and switching means operated by said responsive structure selectively to connect one or the other of said contact elements to said link circuit.

3. An electrical system for determining all positions of a member capable of more than 360 of movement comprising a slide wire having an angular extent of moreethan 360, contact structure therefor mechanically coupled to said member and having contact elements constructed and arranged individually to engage the overlapping portions of said slide wire, a receiving slide wire less than 360 in angular extent, a transmission circuit between said slide wires, and switching means for selectively connecting one or the other of said'contact elements to said transmission circuit. r

4. An electrical measuring system comprising a transmitting station, areceiving station, a link circuit between said stations, a slide wire at said transmitting station extending more than 360 and having a low potential portion overlapping a higher potential portion, contact structure having contact elements for engaging said slide wire,

" one of said elements engaging said low potential portion while the other engages said high potential portion, structure responsive to changes of a condition for eifecting relative rotation of said slide wire and contact structure of more than 360, switching means operated by said responsive structure selectively to connect one or the other of said contact elements to said link circuit, including a lost motion connection to avoid repeated operation of said switching means for oscillation of said responsive structure within a narrow range of movement.

5. An electrical measuring system comprising a receiving potentiometer, a transmitting potentiometer, a link circuit between said potentiometers, said transmitting potentiometer comprising a slide-wire of more than 360 in angular extent, and having overlapping end portions, contract structure therefor having contact elements constructed and arranged individually to engage said end portions, structure for moving said contact structure for more than 360, and switching means for selectively connecting one or the other of said contact elements to said link circuit.

6. A electrical measuring system comprising a Wheatstone bridge having two arms'at a transmittingstation and two arms at a receiving station, said transmitting arms comprising a slide wire of more than 360? in angular extent and having overlapping end portions, contact structure therefor having contact elements constructed and arranged individually to engage said end portions, structure for moving said contact structure for more than 360, and switching means for selectively connecting one or the other of said contact elements to a conjugate conductor of the bridge extending between said stations.

'7. An electrical measuring system comprising a slide-wire having arcuate sections of less than 360 staggered to complete more than 360, contact structure therefor comprising contact elements constructed and arranged individually to engage said different sections to efiect continuous contact between said slide wire and said contact structure, a transmission circuit, and switching means for selectively connecting one or the other of said contact elements to said transmission circuit.

8. An electrical measuring system comprising a slide-wire having arcuate sections of less than 360 staggered to complete more than 360, contact structure therefor comprising contact elements constructed and arranged individually to engage said different sections to efiect continuous contact between said slide wire and said contact structure, a transmission circuit, means for eifecting relative movement of said slide wire to said contact structure of more than 360, and means for effecting connection of said slide wire to said transmission circuit for all relative positions of said contact structure comprising switching means'operated by said first means for transferring connection of said transmission circuit from a contact approaching a gap of its slide-wire section to a contact engaging a slide wire section bridging said gap.

' said sections, an impedance between the low potential ends of said sections, said impedances being of such magnitude that within the region between the low potential end of said second section and the high potential end of said first section, said contact elements are at the same potential.

10. An electrical measuring system comprising a potentiometer slide wire having sections of less than 360 staggered and overlapping to complete more than 360, contact structure therefor comprising contact elements constructed and arranged individually to engage said sections,

means for effecting rotation of said slide wire relative to said contact structure of more than 360, a source of current, connections for connecting said sections in parallel across said source, and resistances connected respectively between the high potential end of one section and one terminal of said source and between the low potential end of the other section and the other terminal of said source, said resistances being of such magnitude that said contact elements for a substantial part of 360 are at the same potential.

11. An electrical measuring system comprising a Wheatstone bridge slide-wire having sections of less than 360 staggered and overlapping to complete more than 360, contact structure therefor comprising contact elements constructed and arranged individually to engage said sections, means for effecting rotation of said slide wire relative to said contact structure of more'than 360, connections for connecting said sections in parallel between conjugate points of said bridge, and

impedances included respectively in the connection from the high end of one section to one of said conjugate points and in the connection from the low end of the other section to the other of said conjugate points, and of such magnitude that said contact elements are at the same potential for a substantial part of 360.

12. An electrical measuring system comprising a transmitting system including a slide wire at said transmitting station of angular extent greater than 360, contact structure therefor, rotatable structure for effecting relative rotation of said slide wire and contact structure of more than 360, a receiving system comprising a slide wire at said receiving station connected to said first slide wire for determining at said receiving station the position of said rotatable structurewithin a complete revolution, and means at said receiving station operated by means included in one of said systems to integrate the revolutions of said rotatable structure.

13. An electrical measuring system comprising a transmitting station, a receiving station, a link circuit between said stations, a slide wire at said transmitting station having an angular extent in excess of 360, contact structure therefor including contact elements one or the other of which engages said slide wire depending upon the relative position of said slide wire and contact structure, rotatable structure for effecting relative movement of said slide wire and contact structure of more than 360, switching means operated by said rotatable structure to eflect transfer of a link circuit connection from one of said contact elements 'to the other at predetermined positions of said contact structure, a self-balancing recorder at said receiving station, a reversible step-by-step device at said receiving station, and

means for controlling said device to integrate the revolutions of said rotatable structure.

14. An electrical measuring system comprising a transmitting station, a receiving station, a link circuit between said stations, a slide wire at said transmitting station having an angular extent in excess of 360, contact structure therefor ineluding contact elements one or the other of which engages said slide wire depending upon the relative position of said slide wire and conv15 with its direction of rotation and for each com- ,plete revolution to control said step-by-step-device for integration of the revolutions of said rotatable structure.

15. An electrical measuring system comprising 20 a slide-wire having arcuate sections of less than 360 staggered to complete more than 360, contact structure therefor comprising contact elements adapted to engage said difierent sections, a source of current, means for connecting said 25 sections in series to said source of current, a transmission circuit, and switching means for selectively connecting one or the other of said contact elements to said transmission circuit.

16. An electrical telemetric system comprising 30 a transmitting system including a transmitting element capable of unlimited revolutions in either direction, and means controlled thereby to prov duce an electrical eflect whose magnitude is uniquely. representative of the displacement of said structure for more than 360", a receiving system including means responsive to said eflfect for determination of the displacement of said member, and a link circuit of not more than three conductors for connecting said transmitting system to said receiving system.

17. An electrical telemetric system comprising a transmitting system including a transmitting element capable of unlimited revolutions in either direction, and means controlled thereby to produce an electrical effect whose magnitude is uniquely representative of the displacement of element capable of unlimited revolutions in either direction, and means controlled thereby to produce an electrical eflect whose magnitude is uniquely representative of the displacement of said structure for more than 360, a receiving system including means responsive to saidefiect,

structure controlled by said responsive means to indicate the position of said element and having a limited range of movement, a link circuit of not more than three conductors for connecting said transmitting system to said receiving system and integrating means controlled by said structure to integrate the revolutions of said element.

WILIJAM R. SCHOFIELD, JR. 

